Offset erasing fluid



United States Patent 3,275,563 OFFSET ERASING FLUID George M. Ort, Chicago, IlL, assignor to A. B. Dick Company, Niles, Ill., a corporation of Illinois No Drawing. Filed Aug. 3, 1962, Ser. No. 214,476 3 Claims. (Cl. 252-171) This invention relates to an erasing fluid for use in conjunction with offset printing. In particular, the fluid is adapted for use on masters which are to be employed in lithographic printing operations.

In one widely employed technique for producing lithographic masters, a paper backing sheet is provided with a suitable hydrophilic coating. For example, a coating comprising a hydrophilic colloid composition which is adapted to receive greasy or oily imaging materials is utilized to a large extent. The image material received on the coated masters is receptive to ink used in the reproduction processes whereby a master suitable for lithographic reproduction is obtained.

In applying to the lithographic sheets the information which is to be reproduced, use can be made of a typewriter ribbon which contains the greasy or oily ink receptive materials. With the lithographic sheet disposed in a typewriter, impact of the typewriter keys will result in transfer of the greasy or oily materials in the ribbon to the sheet. Accordingly, ink receptive areas corresponding to the letters, numbers or other characters on the keys will be formed on the otherwise hydrophilic sheet.

It is desirable to provide means for correcting typing errors or for making changes on the masters so that there is no need for retyping a complete new master when errors are found or changes are necessary. It is also desirable to provide a means for changes in image areas on a master in such a manner that the change will not be apparent in the copy produced. It is important to provide materials for making changes which will not alter the hydrophilic characteristics of the masters so that correct reproductions will be possible after changing of the image areas. Finally, it is desirable to provide materials for making changes which can be used while the master remains in the typewriter -and which operate quickly in order to avoid prolonged interruption of the typing operation.

Various methods have been proposed for use in the alteration of offset masters. Thus, machanical means, such as erasers, have been tried but have not been satisfactory, since these means tend to remove the hydrophilic coatings on the masters or to otherwise dam-age the masters so that high quality reproduction is not possible. The prior art has also proposed erasing fluids. However, in some cases, these fluids have not been effective to completely remove the desired image areas. In other instances, known erasing fluids remove the image areas, but at the same time alter the characteristics of the master to the extent that it will not receive a suitable new image area or to the extent that satisfactory reproduction is not possible.

It is an object of this invention to provide an erasing fluid which is highly satisfactory for use on masters which are to be employed in lithographic printing operations.

It is an additional object of this invention to provide an erasing fluid of the type described which effectively removes all portions of the ink receptive imaging materials in areas of a master which are to be changed, and which accomplishes the removal in a simple manner without dam-age to the master whereby a new image can be formed thereon so that copy of high quality can be provided.

These and other objects of this invention will appear hereinafter, and it will be understood that the specific examples set forth in the following specification are provided for purposes of illustration and not by way of limitation.

The erasing fluid of this invention generally comprises from 50 to 70 volume percent of a chlorinated solvent and 3,275,563 Patented Sept. 27, 1966 "ice from 30 to 50 volume percent of a solution of a hydrated salt of a multivalent metal in its higher oxidation state in an alcohol. It has been found that particularly satisfactory results are achieved when the solution includes stannic chloride-pentahydrate in n-propanol. In addition to n-propanol, the present invention contemplates the use of other alcohols, such as ethanol, methanol and butanol. The salt concentration in the alcohol selected preferably ranges from 0.02 to 0.2 gm./ml.

One preferred erasing fluid consists of about 61 volume percent chloroform and about 39 volume percent of an npropanol solution containing about 0.55 gm./ml. of stannic chloride-pentahydrate. Other preferred combinations contain about 60 volume percent of a chlorinated solvent such as methyl chloroform, methylene chloride, or trichloroethylene, and about 40 volume percent of an alcohol solution including the hydrated salt of stannic chloride or ferric chloride.

The erasing fluid is particularly suitable for removing a typewritten image made on an offset master. The image, which consists of an ink receptive area, can be removed with the fluid of this invention without damage to the master. Therefore, a new typewritten image can be formed on the master and there will be virtually no evidence of the correction when the copy produced by the master is studied.

In applying the fluid, a cotton swab can be employed. The swab should be liberally saturated with the fluid a few seconds before use and the fluid is then applied to the image area in an amount sufficient to provide for complete removal thereof. The fluid will dry in a relatively short time and, therefore, there: is no need for a prolonged interruption of the typing operation. Furthermore, since a swabbing technique is employed, the operation can take place while the master remains in the typewriter.

The following represent specific examples of an erasing fluid prepared in accordance with this invention:

Example 1 Chloroform 53.6 Solution of SnCl -5H O in n-propanol (0.055 grn./

ml. of SnCl -5H O) 33.7

Example 11 Chloroform 59.0 Solution of FeCl -6H O in methanol (0.13 gm./ml.

of FeCl -6H O) 38.0

Example Ill Methyl chloroform 30.5 Solution of SnCl -5H O in n-propanol (0.055 gm./

ml. of SNCl -5H O) 19.5

Example IV Methylene chloride 30.5 Solution of SnCl -5H O in n-propanol. (0.055 gm./

ml. of SnCl -5H O) 19.5

Example V Trichloroethylene 30.5 Solution of SnCl -5H O in n-propanol. (0.055 gm./

ml. of SnCl -5H O) 19.5

Solutions similar in nature to the above as well as those represented by the specific examples have been found eminently suitable for the intended purposes. The ability to remove an existing image without detracting from the ability to receive a new ink receptive .image and without otherwise damaging the master represent particularly notable characteristics of the erasing fluids.

The particular tin and iron salts employed have been found especially satisfactory. However, other salts of multivalent metals in their higher oxidation state, and prepared with various inorganic acids, are also contemplated.

It will be understood that various modifications may be made in the above described erasing fiuids which provide the characteristics of this invention without departing from the spirit thereof, particularly as defined in the following claims.

I claim:

1. A method for removing ink-receptive imaging material applied to the imaged areas of an offset master without altering the ink-repelling characteristics of areas contacted by said fluid in the vicinity of said imaged areas, comprising applying an erasing fluid to said imaged areas in which the fluid consists essentially of from 5070 volume percent of a chlorinated hydrocarbon solvent and 1 from 3050 volume percent of a solution of a hydrated salt selected from the group consisting of stannic chloride and ferric chloride and in which the salt is present in an amount within the range of 0.02 to 0.2 grams per ml. in a lower aliphatic alcohol.

2. The method as claimed in claim 1 in which the chlorinated solvent is selected from the group consisting of chloroform, methylene chloride, and trichloroethylene.

3. The method as claimed in claim 1 in which the lower aliphatic alcohol is selected from the group consisting of n-propanol, ethanol, methanol, and butanol.

References Cited by the Examiner UNITED STATES PATENTS 2,907,656 10/1959 Geese 252-164 XR 10 2,999,816 9/1961 Bennett et a1 252-171 XR 3,051,609 8/1962 Grossmann et al. 13440 XR OTHER REFERENCES The Condensed Chem. Dict., vol. 6, Reinhold Publishing Co., 1961, pp. 488 and 1069.

LEON D. ROSDOL, Primary Examiner.

JULIUS GREENWALD, ALBERT T. MEYERS,

Examiners.

W. E. SCHULZ, Assistant Examiner. 

1. A METHOD FOR REMOVING INK-RECEPTIVE IMAGING MATERIAL APPLIED TO THE IMAGED AREAS OF AN OFFSET MASTER WITH OUT ALTERING THE INK-REPELLING CHARACTERISTICS OF AREAS CONTRACTED BY SAID FLUID IN THE VICINITY OF SAID IMAGED AREAS, COMPRISING APPLYING AN ERASING FLUID TO SAID IMAGED AREAS IN WHICH THE FLUID CONSISTS ESSENTIALLY OF FROM 50070 VOLUME PERCENT OF A CHLORINATED HYDROCARBON SOLVENT AND FROM 30-50 VOLUME PERCENT OF A SOLUTION OF A HYDRATED SALT SELECTED FROM THE GROUP CONSISTING OF STANNIC CHLORIDE AND FERRIC CHLORIDE AND IN WHICH THE SALT IS PRESENT IN AN AMOUNT WITHOUT THE RANGE OF 0.02 TO 0.2 GRAMS PER ML. IN A LOWER ALIPHATIC ALCOHOL. 